Wine (originally an acronym for "Wine Is Not an Emulator") is a compatibility layer capable of running Windows applications on several POSIX-compliant operating systems, such as Linux, Mac OSX, & BSD. Instead of simulating internal Windows logic like a virtual machine or emulator, Wine translates Windows API calls into POSIX calls on-the-fly, eliminating the performance and memory penalties of other methods and allowing you to cleanly integrate Windows applications into your desktop.

Wine began in 1993 under the initial coordination of Bob Amstadt as a way to support running Windows 3.1 programs on Linux. Very early on, leadership over Wine's development passed to Alexandre Julliard, who has managed the project ever since. Over the years, as the Windows API and applications have evolved to take advantage of new hardware and software, Wine has adapted to support new features, all while being ported to other OSes, becoming more stable, and providing a better user-experience.

An ambitious project by definition, work on Wine would steadily continue for 15 years before the program finally reached v1.0, the first stable release, in 2008. Several releases later, Wine is still under active development today, and although there is more work to be done, millions of people are estimated to use Wine to run their Windows software on the OS of their choice.

Site: http://www.winehq.org/
